302 PHYSIOLOGY. 



prevent the coagulation of the blood by introducing an alkaline solu- 

 tion into the points of the apparatus where the blood must penetrate. 

 The liquid most commonly used is a saturated solution of sodium 

 carbonate. 



In 1847 the study of arterial tension entered a new phase, thanks 

 to the use made by C. Ludwig of the apparatuses with continuous indi- 

 cations to measure the variations which that tension undergoes under 

 the influence of many conditions. The instrument that he used is 



Fig. 101. Cardiac Manometer. (LAHOUSSE.) 



A and B, Two burettes of glass able to communicate with the bifurcated 

 cannula, C, by the aid of a stop-cock with three openings. M, Small mercury 

 manometer. 1), Smoked drum. 



known as the kymograph, or "wave-writer." In brief, it consists of a 

 U-shaped manometer, in the open limb of which a light float is placed 

 upon the surface of the mercury. A writing-style is placed trans- 

 versely upon the free end of the float, which inscribes its movements, 

 representing the oscillations of the mercury, upon a cylinder which 

 revolves at a uniform rate by reason of clock-work. There is recorded 

 not only the height, but its pulsatile and respiratory oscillations. 



In looking at a blood-pressure tracing we find that the large 

 undulations are produced by respiratory movements. Usually the 

 ascent is caused by inspiration, the descent by expiration. Each of 



